The invention pertains to a process of removing contaminants from olefin feedstocks using sorbents. In a preferred embodiment, phosphorus-containing impurities, most preferably organophosphines and/or organophosphine oxides, are removed from the olefin feedstock using an acidic or a neutral sorbent. The sorbent preferably is selected from the group consisting of an acidic ion exchange resin, an acidic zeolite, an acidic alumina, a neutral alumina, and an activated carbon. Preferred olefin feedstocks are those made by oligomerizing ethylene to linear olefins having from about 6 to about 36 carbon atoms, preferably from about 11 to about 20 carbon atoms, and most preferably from about 14 to about 18 carbon atoms.
Depending upon the method of their production, olefin feedstocks may comprise a variety of impurities. Impurities found in olefins that are produced by oligomerization of ethylene units include phosphorous-containing impurities, including but not necessarily limited to organophosphines and organophosphine oxides. These phosphorous-containing impurities are largely removed from many olefin streams during the process of distillation to separate various xe2x80x9ccutsxe2x80x9d of olefins. Unfortunately, the organophosphines and organophosphine oxides found in C14-C18 streams tend to codistill with the C14-C18 in the product, making it difficult, if not impossible to remove these phosphine impurities by simple distillation.
C6-C36 olefins have utility in the fields of paper and pulp processing, drilling fluids, and machine or metal working oils. Alcohols of such olefins have commercial importance in a variety of applications, including detergents, soaps, surfactants, and freeze point depressants in lubricating oils. These alcohols are produced by a number of commercial processes, such as by oxo or hydroformylation of long chain olefins. In many of these applications, the olefin feedstocks are treated using acid catalysts.
Unfortunately, any phosphorus-containing impurities in these olefin feedstocks will negatively affect acid catalysts. The phosphorous-containing moieties are basic in nature and will neutralize the active acid sites of the catalyst, which lowers catalyst activity and performance. The organophosphine moeities may even cause the olefins to oligomerize into undesirable forms.
Methods are needed to reduce the phosphorous-content of olefin feedstocks.
The present invention provides a process for purifying an olefin feed comprising a content of phosphorus-containing impurities. The process comprises contacting the olefin feed with a sorbent selected from the group consisting of an acidic ion exchange resin, an acidic zeolite, an acidic alumina, a neutral alumina, and an activated carbon under conditions and for a time effective to reduce the content of phosphorus-containing impurities and to produce a purified olefin feed.
The present invention provides a process and sorbents which efficiently and effectively reduce the content of phosphorous-containing impurities in olefin streams. In a preferred embodiment, the content is reduced to about 1 ppm or less, preferably about 0.5 ppm or less, most preferably to about 0.1 ppm or less. Given sufficient run time, the sorbents reduce the content of phosphorous-containing impurities in the olefin stream to parts per billion (ppb) levels. In a preferred embodiment the sorbents of the present invention may be used to remove dienes from the olefin stream.
The invention may be used to treat substantially any olefin stream. Preferred olefin streams are linear olefin streams made by oligomerizing ethylene. Some of the known processes for oligomerizing ethylene use organophosphorus compounds that result in phosphorus as a contaminant in the resulting olefin stream. A preferred commercially available olefin feed for the treatment of the present invention is the product marketed in the United States by Shell Chemical Company under the trademark NEODENE(copyright). In a preferred embodiment, the olefin feedstock is treated before exposure to an acid catalyst, or before exposure to other conditions which would be adversely affected by the basic nature of phosphorus-containing contaminants.
In a most preferred embodiment, the olefin stream is the feedstock for the skeletal isomerization catalyst used in the method described in U.S. Pat. No. 5,849,960, which has been incorporated herein by reference. The olefins used in the feed to this skeletal isomerization catalyst are mono-olefins having at least 6 carbon atoms, preferably having from about 11 to about 20 carbon atoms, and most preferably having from about 14 to about 18 carbon atoms.
In general, the olefins in the feed to the skeletal isomerization catalyst are predominately linear. While the olefin feed can contain some branched olefins, the olefin feed processed for skeletal isomerization preferably contains greater than about 50 percent, more preferably greater than about 70 percent, and most preferably greater than about 80 mole percent or more of linear olefin molecules.
The olefin feed to the skeletal isomerization catalyst does not consist of 100% olefins, and usually contains a distribution of mono-olefins having different carbon lengths, with at least 50 wt. % of the olefins being within the stated carbon chain range or digit, however specified. Preferably, the olefin feed will contain greater than 70 wt. %, more preferably about 80 wt. % or more of mono-olefins in a specified carbon number range, the remainder of the product being olefins of other carbon number or carbon structure, diolefins, paraffins, aromatics, and other impurities resulting from the synthesis process. The location of the double bond is not limited. The olefin feed composition may comprise alpha olefins, internal olefins, or a mixture thereof.
The sorbent of the present invention may be substantially any suitable sorbent capable of sorbing phosphorus-containing impurities, preferably neutral and acidic sorbents, most preferably acidic sorbents. Suitable neutral sorbents include neutral aluminas, activated carbons, and metal impregnated activated carbons, such as BARNEBEY CE, a silver impregnated carbon available from Barnebey and Sutcliffe. Suitable acidic sorbents include, but are not necessarily limited to acidic ion exchange resins and acidic aluminas. Suitable commercially available aluminas include, but are not necessarily limited to acidic and neutral activated aluminas, such as those available from Aldrich Chemical Co. and Selecto Scientific Co. Also suitable are the modified aluminas, such as SELEXSORB CDO 200, SELEXSORB CDX, AND SELEXSORB CD. These aluminas are modified to improve the sorption of polar organics, and are commercially available from Alcoa Industrial Chemicals. Also suitable are acidic ion exchange resins, such as AMBERLYST 15 RESIN, available from Rohm and Haas Chemical Co.
The surface area of the sorbent is not critical, but preferably is at least about 10 m2/g in order to provide sufficient contact between the sorbent and the olefin stream. In a preferred embodiment, the sorbent has a surface area of from about 100 m2/g to about 900 m2/g. It is preferred for the sorbent particles to be as small as possible; however, if the size of the particles is too small, the pressure drop through the bed becomes too large. Very small particles also are difficult to retain in the sorbent bed. The particles may have substantially any form, including but not necessarily limited to spherical form, tablet form, cylindrical form, multilobed cylindrical forms, and their corresponding hollow counterparts. In a preferred embodiment, the particles have a diameter of from about 50 mesh to about 6 mm, preferably about 0.8 mm ({fraction (1/32)} inch) to about 1.6 mm ({fraction (1/16)} inch), most preferably about 0.8 mm. The length of the particles is not critical, with suitable lengths including, but not necessarily limited to less than about 10 mm, preferably from about 3 mm to about 5 mm.
In a preferred embodiment, the sorbent is an acidic ion exchange resin, most preferably AMBERLYST 15, which generally may be used as received from the supplier.
In another preferred embodiment, the sorbent is an alumina extrudate which is extruded as a paste using an acidic or neutral alumina powder. The xe2x80x9cpastexe2x80x9d is extruded or otherwise molded into a multilobed cylindrical form. The resulting material preferably is dried at temperatures of at least about 100xc2x0 C. and calcined at about 500xc2x0 C. or more in the presence of flowing air in a muffle furnace or purged high temperature air drier or rotary calciner.
Preferably, the olefin feedstock is contacted in the liquid phase in a reaction zone with the sorbent of the present invention at effective process conditions to reduce the content of phosphorous-containing impurities in the feedstock, i.e., an effective temperature, pressure, and LHSV (Liquid Hourly Space Velocity). A preferred embodiment of a reactor system for the process is an upflow or downflow fixed bed reactor. An upflow reactor is preferred for better wetting of the sorbent bed. The temperature employed may vary. Although not limited to a particular temperature, best results will be obtained if the process is conducted at temperatures of from about 0xc2x0 C. to about 100xc2x0 C., preferably from about 10xc2x0 C. to about 50xc2x0 C. The pressures may vary over a range including but not limited to autogeneous pressures and pressures in the range of from about 0.01 MPa to about 50 MPa. A preferred pressure is in the range of from about 0.1 MPa to about 10 MPa. Pressures outside of the stated ranges may be used and are not excluded from the scope of the invention.
The feedstock may flow at a wide range of liquid hourly space velocities (LHSV), defined as liquid feed per hour per volume of sorbent. The LHSV is calculated as follows:   feed  xc3x97            Volume      ⁢              xe2x80x83            ⁢      of      ⁢              xe2x80x83            ⁢      olefin      ⁢              xe2x80x83            ⁢      containing      ⁢              xe2x80x83            ⁢      1              Volume      ⁢              xe2x80x83            ⁢      of      ⁢              xe2x80x83            ⁢      sorbent      ⁢              xe2x80x83            ⁢      hr      
The lower the LHSV, the greater will be the reduction in content of phosphorus-containing impurities in the feedstock. The LHSV generally is from about 0.01 hr to about 10 hrxe2x88x921, preferably from about 0.1 hrxe2x88x921 to about 1 hrxe2x88x921.
The process is continued for a period of time sufficient to achieve a desired reduction in the content of phosphorus-containing impurities in the olefin stream. The content of phosphorus-containing impurities preferably is reduced to about 1 ppm or less, most preferably to about 0.1 ppm or less. The reaction cycle time may vary from tenths of seconds to a number of hours. The reaction cycle time is largely determined by the reaction temperature, the pressure, the sorbent selected, the liquid hourly space velocity, and the desired reduction in content of phosphorus containing impurities.
At some point, the sorbent becomes saturated, and must be regenerated. The sorbent may be regenerated by exposing the sorbent to an oxygen-containing atmosphere at a temperature of from about 200xc2x0 C. to about 550xc2x0 C., preferably from about 450xc2x0 C. to about 600xc2x0 C. Suitable oxygen containing atmospheres include, but are not necessarily limited to air, oxygen gas, and a combination of oxygen gas with nitrogen gas. A preferred gas is a commercially available combination comprising about 1% oxygen, with the remainder being nitrogen. After exposure to these increased temperatures for a period of time of from about 0.5 hour to about 100 hours, the bed is cooled to at least about 100xc2x0 C., and preferably to about 25xc2x0 C., or ambient temperature, in order to avoid overheating upon reuse. The cooled bed is purged with nitrogen or air before reuse in the process. Ten regeneration cycles under these conditions have been shown to produce no loss in sorbent capacity. Some slight loss in sorbent capacity was seen beginning after 10 regeneration cycles.
Typical olefin feedstocks comprise from about 100 ppm to about 2000 ppm dienes that tend to lower the efficiency of skeletal isomerization catalysts. The sorbents of the present invention are useful for sorbing dienes from the feedstream, both before and after the olefin feedstock contacts the skeletal isomerization catalyst. In a preferred embodiment, the sorbent of the present invention may be used to sorb dienes from initial olefin streams before contact with the isomerization catalyst in addition to lowering the phosphorus content of the olefin stream. Substantially all of the sorbents listed herein may be used for this purpose. A preferred sorbent for removing dienes is alumina.
C6 to C36 olefins have a variety of uses, including but not necessarily limited to uses in paper processing, drilling fluids, and machine or metal working. In a preferred embodiment, the olefin feedstock is converted to branched primary alcohols in the process described in U.S. Pat. No. 5,849,960, incorporated herein by reference. Most preferably, the olefin feedstock is treated before the olefins are fed to a skeletal isomerization catalyst, as described in U.S. Pat. No. 5,849,960. A preferred skeletal isomerization catalyst for use in conjunction with the present invention is a hydrogen ferrierite catalyst, as described in U.S. Pat. No. 5,510,306, incorporated herein by reference.
In a preferred embodiment, the skeletally isomerized olefins are converted to any of a broad range of surfactants, including nonionic, anionic, cationic, and amphoteric surfactants, with a degree of branching of at least 1.0. The skeletally isomerized olefins serve as a surfactant intermediate. Specifically, the skeletally isomerized olefins serve as the hydrophobic moiety of the surfactant molecule, while the moiety added to the olefin during the conversion process serves as the hydrophile.